Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$135.60	5.693%	$143.3197	$143.32	$143.30	$143.30
Purchase #2	$74.43	6.268%	$79.0953	$79.10	$79.10	$79.10
Purchase #3	$99.25	12.521%	$111.6771	$111.68	$111.70	$111.70
Purchase #4	$234.27	10.192%	$258.1468	$258.15	$258.15	$258.10
Purchase #5	$130.36	4.748%	$136.5495	$136.55	$136.55	$136.50
Purchase #6	$111.49	4.515%	$116.5238	$116.52	$116.50	$116.50
Purchase #7	$129.81	6.185%	$137.8387	$137.84	$137.85	$137.80
7 purchase totals =	$915.21		$983.1509	$983.16	$983.15	$983.00